Electric contact



May 7, 19460 F. R, HENSEL ET AL 2,400,003 IILECTRIC CONTACT Filed April16, 1945 4 Mam/VF ca/vT/icT z POSIT/VE CONT/{6f Fiahz Z flrzsel Kennel];Z- Emma) INVENTORS BY 2 Z z i 2 Patent ed May 7, 1946 W. Wiggs,Indianapolis, Ind., a'sslgnors to P.-R. Mallory dt 00., Inc.,Indianapolis, Ind., a corporation of Delaware Application April 1c,1943, Serial No. 483,334

.2 Claims.

This invention relates to electric contacts and the composition thereof.

An object of the invention is to improve electric contacts and contactcompositions.

Other objects of the invention will be apparent from the description andclaims.

The present invention contemplates an electrical contact combination orset in which the positheir properties. Likewise, up to a few percent oftive contact is formed from gold or a gold base alloy containing indiumand the negative contact is formed predominately from silver or fromsilver base alloys. Such contact sets are characterized by highcorrosion resistance and can be used in industrial atmospheres withoutthe formation of a tarnish film-thereon which would increase theelectrical resistanceof the contacts. The contact combination is usefulfor such appli cations as pressure exerting welding electrodes and aswell as electric make-and-break contacts since such contacts have goodtensile and compressive strength as well as a high degree of hardness.

The wear resistant properties of the contact, along with its otherproperties render it useful also in high speed relays where thefrequency of make and break operations is extremely high.

In the drawing the figure shows a pair of cooperating contacts embodyingfeatures of the present invention. a

The contacts of the present invention may contain ' Per cent Indium 0.5to 25 Gold Balance The preferred range of composition is Per cent Indium0.5 to 8.5

Gold Balance The gold used may be either pure gold or one of 20%, andhence are sometimes present in proportions still higher than if thehigher carat golds were used in making the compositions.

Up ,to a few percent of iron group metals, particularly nickel or cobaltmay be added to the compositions in some cases to further improveplatinum or palladium may be present.

Other ingredients which are commonly alloyed with gold, copper andsilver may also be present, such as tin, manganese and silicon. In anycase the percentage of sold will exceed by weight and the elements otherthan indium may be presentup to about 30%. Manganese, if present, isused in proportions up to 2% by weight.

Examples of electric contact and welding electrode compositions whichare suitable are:

l (a) Indium -3 g? Gold 97.5 (b) Indium 5 Gold..- 95 (c) Indium '8 Gold-92 (a) Indium 5 Gold '71 Silver 24 (e) Indium 5 G Silver 12.5 Copper12.5 (,f') Indium 5 Gold "70 Copper 25 (g) Indium 8 Gold 69 Copper 3Nickel 15 Zinc 5 One of the problems encountered in make-andbreakcontacts is the tendency of material to transfer from the face of onecontact to the other contact and thereby build up a projection on thesecond contact leaving a pitted or eroded area on the first contact. Thecontact compositions of the present invention are remarkably free ofsuch tendency to transfer in both A. C. and D. C. circuits where eitherone or both contacts is formed of this material.

While the alloy of this invention may be used for contacts of eitherpolarity they are most useful for the positive contact.

Suitable compositions or alloys for the negative side. of the contactpair are pure silver and silver alloys, for example cent Palladium orplatinum 0.5 to 5 Silver Balance The gold base alloys containing indiumcan be manufactured by standard procedures such as melting, casting andthen rolling or drawing, according to the type of contact or weldingelectrode tip to be fabricated.

The alloys of gold and indium iorm a solid solution up to about 8.5%indium by weight. The solid solubility of indium in gold decreases withtemperature and therefore alloys may be'heat treated in order toincrease the electrical conductivity or the physical properties. Such aheat treating may consist in quenching from 400 to 700 0., dependingupon the composition, and the subsequent aging temperature may vary from150 to 400 C. The aging time may vary from several minutes up to severalhours, depending upon the ageing temperature and weight of the piece.

Referring to the drawing a pair of ctr-operating contacts for D. C.operation are shown comprising a positive contact i formed of agold-indium alloy cooperating with a negative contact 3 formed of silveror silver alloy. The contacts are mounted on operating arms 2 and lrespectively, which are arranged in a relay, switch or similar device toopen and close the contacts in order to make and break a D. C. circuit,the positive ter- 1. An electric contact combination wherein thepositivecontact is formed of a gold base alloy containing indium and thenegative contact is formed of a material from the group comprising puresilver and silver alloys.

2. An electric contact combination wherein the positive contact isformed of a 801d base alloy containing indium, and the negative contactis formed predominantly of silver.

FRANZ R. HENSEL.

H L. WT. JAMES W. WIGGS.

